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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence

A Sedrakyan, SL Normand, S Dabic, S Jacobs, S Graves, and D Marinac-Dabic.

Review published: 2011.

CRD summary

The authors concluded that there was limited evidence regarding comparative effectiveness of various hip implant bearings and the results did not indicate any advantage for metal on metal or ceramic on ceramic implants compared with traditional bearings. Given the poor quality of the included comparative studies and the general lack of data, the authors' cautious conclusions seem appropriate.

Authors' objectives

To compare the safety and effectiveness of implantable hip devices with different bearing surfaces.


MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) were searched between 1995 and June 2011 for publications in English; search terms were reported. Reference lists of trials and reviews were searched manually. Annual reports of major registries, summaries of safety and effectiveness for pre-market application and mandated post-market studies at the US Food and Drug Administration were consulted for relevant data.

Study selection

Comparative clinical trials that were of adults who underwent conventional hip replacement were eligible for inclusion. Eligible trials used combinations of bearings (such as metal on metal and ceramic on ceramic) and reported functional outcomes, occurrence of revisions or both.

Most of the included comparative studies were conducted in USA. Some studies were in the UK and other European countries, South Korea, Canada and Japan. Mean age of patients ranged from 42 to 71 years. Where reported, between 26% and 88% of participants were female. The most prominent patient diagnosis was osteoarthritis. Some patients had avascular necrosis. Comparative studies compared traditional bearings (ceramic on polyethylene and metal on polyethylene) to each other, alternative bearings (such as metal on metal and ceramic on ceramic) to each other or compared traditional versus alternative bearings. Most studies included multiple surgeons. Surgical procedures were conducted between 1995 and 2008. Functional outcomes were assessed using the Harris hip score or general quality of life measures such as SF-12.

At least two reviewers performed the search.

Assessment of study quality

Included studies were assessed on overall risk of bias according to method of randomisation, allocation concealment, blinding of patients and outcome assessors and intention-to-treat analysis. Observational studies were assessed on quality according to STROBE criteria. Studies were classified as being high quality (met all criteria), moderate (moderate to high or moderate to low dependent on proximity to high or low quality) or low quality (met none of the criteria).

Data extraction

Two reviewers independently extracted data on the number of events (revision surgery and reported dislocation), relative risks (RRs) and their 95% confidence intervals (CIs), and p values. Means and, where reported, standard deviations (SDs) and ranges were extracted for functional outcome scores to calculate mean differences with 95% CIs. Where reported, both baseline and follow-up measurements were extracted. Where appropriate, standard deviations were imputed for trials. Discrepancies were resolved by the senior author.

Methods of synthesis

Clinical heterogeneity was assessed by comparison of trial populations and outcome data. Where meta-analyses were not possible, a narrative synthesis was presented. Where appropriate, a random-effects model was used to combine mean differences and their 95% CIs for functional outcomes. Statistical heterogeneity was assessed using I2, X2 and Τ2.

Subgroup analyses were conducted by type of traditional bearing surfaces. Where means were imputed for studies, sensitivity analyses were performed to assess the effect of varying estimates of significant difference on the overall estimate of effect.

Results of the review

Eighteen comparative studies (3,139 patients, 3,404 hips) were included in the review. Fifteen studies were randomised controlled trials, two were non-randomised trials and one study included both a randomised and non-randomised arm. Study follow-up ranged from three months to 8.1 years. Four randomised trials were classified as being moderate to high quality, five as moderate quality and six as low quality. Where reported, between 65% and 100% of patients were followed up.

Functional outcomes: Comparison of metal on metal bearings versus metal on polyethylene at two years showed improvements in Harris hip scores associated with metal on polyethylene (-2.4, 95% CI -4.5 to -0.3, I2=0%; four studies). No other comparisons using Harris hip scores were significantly different. Sensitivity analyses did not significantly alter the overall findings. One of six studies that used alternative functional measurement scores showed substantially better functioning with metal on polyethylene compared to metal on metal bearing surfaces.

Surgical revision and dislocation: There were no statistically significant differences in occurrence of surgical revisions or dislocation between metal on metal versus metal on polyethylene bearings (two studies). One of two studies that compared metal on metal with ceramic on polyethylene reported substantially higher occurrence of dislocation in the ceramic on polyethylene group. One of two studies that compared ceramic on ceramic with metal on polyethylene bearings showed substantially lower occurrence of revision in the ceramic on ceramic arms. There were no other significant differences in surgical revision for any other comparison, including ceramic on ceramic versus ceramic on polyethylene (five studies).

Findings from six national registries were reported. These were mixed or conflicted with the comparative study findings. Further details were reported in the review.

Authors' conclusions

There was limited evidence on comparative effectiveness of various hip implant bearings. The results did not indicate any advantage for metal on metal or ceramic on ceramic implants compared with traditional bearings.

CRD commentary

The review question and supporting inclusion criteria were broadly defined. Appropriate sources were searched for relevant studies. The search was restricted to studies in English and the authors acknowledged potential for language bias as a result of this. Screening of the literature and data extraction were performed in duplicate; it was unclear whether this was also true for quality assessment, so reviewer error and bias could not be ruled out. Appropriate criteria were used to assess study quality. Most of the comparative studies were at risk of bias, which the authors acknowledged.

There was considerable clinical and methodological heterogeneity among studies. Methods of synthesis seemed appropriate. There was a general lack of reporting on outcome data. Most studies were underpowered.

Given the poor quality of the included comparative studies and the general lack of data, the authors' cautious conclusions seem appropriate.

Implications of the review for practice and research

Practice: The authors stated that differences in functional outcomes were small and might not be clinically relevant, but may still be valuable to inform future research. They also stated that until high-quality trials were undertaken, national registries provided important real world data on the safety and future comparative safety and effectiveness evaluation.

Research: The authors stated that a large high-quality randomised controlled trial was needed to compare bearing surfaces in total hip replacement before any claims of benefit can be made.


US Food and Drug Administration Centre for Devices and Radiological health.

Bibliographic details

Sedrakyan A, Normand SL, Dabic S, Jacobs S, Graves S, Marinac-Dabic D. Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence. BMJ 2011; 343:d7434. [PMC free article: PMC3226583] [PubMed: 22127517]

Indexing Status

Subject indexing assigned by NLM


Ceramics; Chromium Alloys; Female; Hip Prosthesis /standards; Humans; Joint Diseases /surgery; Male; Polyethylene; Prosthesis Design; Recovery of Function; Reoperation; Safety; Treatment Outcome



Database entry date


Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 22127517

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